According to TCP specifications described in RFC1122 (reference 1), a portion of ICMPv6 errors such as “Destination Unreachable: no route to destination (ICMP type-1: code 0)” might be “soft errors” such as temporary errors. Since the error is a “soft” or temporary error, the TCP connection is not immediately aborted even if this notification is received and attempts to establish a connection are repeated until the retry count is exceeded. Therefore no TCP connection on IPv4 is established even when a host operating on IPv4/v6 dual stack confirms that another host cannot be reached by communication on IPv6 due to an ICMPv6 error “Destination Unreachable: no route to destination”. Instead, repeated attempts are made to establish a TCP connection on IPv6 up to the upper time out limit, causing the problem that constant delays occur as described in Section 3.2 in the draft-ietf-tcpm-tcp-soft-errors-01.txt (reference 2).
A technique to resolve this problem is disclosed in Section 4 of the draft-ietf-tcpm-tcp-soft-errors-01.txt (reference 2) by changing the TCP in the terminal to promptly quit the connection if a soft error is received just in the phase where establishing the connection.
Reference 1: Braden, R., “Requirements for Internet Hosts—Communication Layers”, STD-3, RFC 1122, October 1989.
Reference 2: F. Gont., “TCP's Reaction to Soft Errors”, Internet-Draft, draft-ietf-tcpm-tcp-soft-errors-01.txt. August 2006.